The present invention relates to an LNG-freon generation system, where LNG means "liquefied natural gas". To be more precise, the present invention concerns a novel generation system that uses freon as a working fluid, which is subjected to cooling by LNG directly or indirectly, pressurized by compressors, vaporized by heating, and which expands to drive a turbine and generates electricity.
The invention aims at moderating the heat pollution caused by the exhaust heat of a conventional steam power plant and the cold pollution caused by the exhaust cold of a vaporizing plant of LNG. To make clear the contribution this invention has on the energy problem, particularly the heat pollution problem on rivers and in seas, the motivation and background of the invention is described in the following.
In industrialized countries, nuclear and conventional steam power plants are located at their coastal areas or along rivers to ensure cooling water supply and to facilitate the disposal of huge amount of warm exhaust, which sometimes causes serious changes in ecology and produces a variety of reasons for opposition movements by citizens.
According to the present technology, a PWR or BWR nuclear power plant has a heat efficiency of 30% to 33%. Nearly 40% of its generated heat is carried into the sea or rivers by warm water through the condenser. For a 1000 MWe BWR power plant, the warm exhaust amounts of 70 tons per second, its temperature being kept 8.degree. C. higher than that of the environment. In Japan for example, an estimate indicates that the discharged warm water from conventional and nuclear power plants in the whole of Japan will reach the amount of 600 billion tons per year toward the end of this century. This huge amount is comparable with the annual rainfall in Japan. Her coastal water will be affected immeasureably. Thus, it is an important issue in any industrial country to moderate the huge heat pollution coming from steam power plants.
Now in most industrial countries, the government faces more or less strong opposition from the public in developing its nuclear power programs. Some countries increase the importation of LNG year by year to compensate for the delay in its nuclear power programs. An example can be seen in Japan, which imported 5 million tons of LNG in 1975 and has a plan to import 30 to 42 million tons of LNG in 1985. The latter (42 million) is in the demand-supply plan drafted by the Energy Investigation Board of the Ministry of International Trade and Industry in December 1975 and the former figure (30 million) is the figure in the revised plan drafted by the same Board in December 1977.
The temperature of LNG is as low as -162.degree. C. under 1 atmosphere, therefore, it has to be vaporized and heated to room temperature before coming into use. More than 200 Kcal is required to obtain 1 Kg of natural gas at room temperature by heating LNG. The gasification of LNG is usually accomplished by heat exchange with sea water. This gasification of LNG discharges 25 thousand tons of cold sea water 8.degree. C. below the environmental temperature in order to have one thousand tons of natural gas at room temperature. Judging from this point, it is obvious that an enormous amount of cold sea water poured into a closed sea, such as Tokyo Bay and Osaka Bay, will cause a serious cold water pollution problem sooner or later.
Stimulated by these pollution problems, the present invention has been conceived to bridge the heat pollution and the cold pollution by circulating a freon as a working fluid. Any difference in temperature should produce some electricity. A typical example is a thermo-couple.